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MMD > Archives > June 1997 > 1997.06.09 > 03Prev  Next


Standard Valve Problem
By Craig Brougher

Sam Harris asks, in regard to his Standard Valve problem:

> Now I need your professional opinion on a few questions before I take any
> further action on this player.
>
> 1.  Will a porous secondary pouch cause the kind of problems I am having?
>
> 2.  Should I seal all pouches in this action?
>
> 3.  Is it safe to say that most all new leather pouches need to be
> sealed?
>
> 4.  What should be used as a sealer?
>
> 5.  How would you apply it?
>
> 6.  If I end up sealing all pouches will I have to adjust valve travel or
>     will that have to be determined after the sealing is complete?

Sam's problem, as stated, was that at low vacuum, his pneumatics seemed
to work, but at higher levels they stopped working on two notes, which
are separated by a note. I don't know how these pouches are staggered
on the board, but #25 and 27 are very close to the break between bass
and tenor. So it might not be valves, at all, but mechanical interference
caused when the striking finger rises quickly and lots of pressure put
on the action. I would definitely check the strikers and the action.

1. First of all, porous pouches will not cause the problem you are
   having at all. However, if you had a small crack or channel between
   pouches somewhere, it could, in some ways, simulate the problem.

2. Sealing the pouches evens the response time--for better or for
   worse. It is doubtful that this will cause anything, unless your
   pouch leak is actually a glue line leak at the pouch. In which case,
   it will cause the very thing you are experiencing-- just like I said
   before-- a proportional "flap" leak.

3. It is always a good idea to seal pouches, to make valve response
   more consistent even in double valve actions, and to preserve the
   pouches.

4. I am familiar with Dow Corning 111 Silicone grease, plus talcum
   powder, after it is fully dry. You should read the archives on how
   to apply this.  There is definitely a "wrong" way to do it.

6. Sealing pouches will cause no further adjustment changes.

I personally do not think you have defined the problem, Sam. I noticed
that you said that when the action was on the bench, the valve pairs
worked like they were supposed to, both on low and high vacuum. The
hisses you hear on the offending valves are your secondaries, unable
to close and seal all the way when actuated. That also makes me wonder
if your problem isn't what I suggested-- the hinge end of the pneumatics
are interfering with their stems, which stick out too far, and the
inside valve disk has too much play. This would cause your problem,
because at low vacuum, the disk wouldn't move very much on the stem,
so the stem doesn't protrude too far and get blocked by the pneumatic.

If you have used plastic glue on the pneumatics, this creates a problem,
because the hinges are not stable, so when the pneumatic is very forceful,
the lower leaf of the pneumatic moves backward. If the tip ends of the
valve stems are touching, when the valves actuate, then they will be
blocked by the pneumatic when under more pressure. On the bench, you
wouldn't see this because the pneumatic isn't lifting anything, but in
the piano, you would not be able to play those notes.

Craig Brougher


(Message sent Mon 9 Jun 1997, 13:34:48 GMT, from time zone GMT.)

Key Words in Subject:  Problem, Standard, Valve

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